Sometimes the scope of a project is left undetermined. This can be, and often is, a mutual arrangement between client and artist. It is agreed the wall can go on and be built longer, later. More retaining walls and terraces can be 'talked' about in the future.
Usually for me the first project is the dry stone 'foot in the door'. Not literally, of course. Good work begets more good work.
But one day, if it there was the right setting for it, I think there could be an opportunity of putting a dry stone foot in the doorway somewhere. And then, of course, it could be gradually added to, in the future.